VB CRC check sum calculation 100

private sub command1 click()dim data() as byte

DIM check digit as integer

dim bytes as long

dim low as boolean

Checksum = -1

Data = strconv(text1, vbfromunicode) bytes = ubound(data).

for i = 0 to bytes.

Low = ture

for j = 1 to 8

If the low bit then checksum = checksum xor data (i) low bit = data (i) and 1

Data (i) = Data (i) 2

next j

next i

text2 = hex (checksum).

end sub

That's pretty much the way the algorithm goes.

Calculation method of CRC checksum:

1. Cyclic check code (CRC code): It is the most commonly used error check code in the field of data communication, and the feature of the bridge is that the length of the information field and the check field can be arbitrarily selected.

2. The basic principle of generating CRC code: any ** composed of binary bit strings can correspond one-to-one with a polynomial with coefficients only the values of '0' and '1'.

For example, the polynomial corresponding to the 1010111 is x6+x4+x2+x+1, and the polynomial is the **101111 corresponding to x5+x3+x2+x+1.

Precautions

It is a convention between the receiver and the sender, that is, a binary number that remains constant throughout the transmission.

On the sender, the generated polynomial is used to modulo 2 the information polynomial by generating a check code. On the receiving side, the received coded polynomial is modulo2 by generating multi-ballast terms, and the error location is detected and determined.

The following conditions should be met: Tsai Lumeng.

1. The highest and lowest digits of the generated polynomial must be 1.

2. When there is an error in any digit of the transmitted information (CRC code), the remainder should not be 0 after the division of the generated polynomial.

3. When there is an error in different bits, the remainder should be different.

4. Continue to divide the remainder, and make the remainder circular.

1. Cyclic check code (CRC code): It is the most commonly used error check code in the field of data communication, which is characterized by the fact that the length of the information field and the check field can be arbitrarily selected.

2. The basic principle of generating CRC code: any ** composed of binary bit strings can correspond one-to-one with a polynomial with coefficients only the values of '0' and '1'.

For example, the polynomial corresponding to the 1010111 is x6+x4+x2+x+1, and the polynomial is the **101111 corresponding to x5+x3+x2+x+1.

If the information bit is known to be 1100, the polynomial g(x) =x3+x+1 is generated, and the CRC code is found.

m(x) =1100 m(x)*x3 = 1100000 g(x) =1011

m(x)*x3 / g(x) =1110 + 010 /1011 r(x) =010

The CRC code is: m(x)*x 3+r(x)=1100000+010=1100010

The principle is: the CRC code is generally generated by splicing the R-bit check bit after the K-bit information bit. The coding steps are as follows:

1) Represent the k-bit information to be encoded as a polynomial m(x).

2) Shift m(x) to the left by r to get m(x)*xr.

3) Remove m(x)*xr with the generative polynomial g(x) of the r+1 bit to get the remainder r(x).

4) Add M(X)*XR and R(X) as module 2 to obtain the CRC code.

I'll give you an example first:

Knowing that the information bit is 1100, the polynomial let g(x) =x3+x+1 is generated, and the crc code is obtained.

m(x) =1100 m(x)*x3 = 1100000 g(x) =1011

m(x)*x3 / g(x) =1110 + 010 /1011 r(x) =010

The CRC code is: m(x)*x 3+r(x)=1100000+010=1100010

The principle of hand slippage is that the CRC code is generally generated by splicing the R-bit check bit after the K-bit information bit. The coding steps are as follows:

1) Represent the k-bit information to be encoded as a polynomial m(x).

2) Shift m(x) to the left by r to get m(x)*xr.

3) Divide m(x)*xr with the polynomial g(x) of the r+1 bit to get the remainder r(x).

4) Add M(X)*XR and R(X) as module 2 to obtain the CRC code.